1. Field of the Invention
The present invention relates to a non-aqueous ink, a printing method that uses the ink, and a method of producing the ink.
2. Description of the Related Art
An inkjet recording system is a printing system in which printing is conducted by spraying a liquid ink with a high degree of fluidity from very fine nozzles, and adhering the ink to a recording medium such as a sheet of paper. These systems enable the printing of high-resolution, high-quality images at high speed and with minimal noise, using a comparatively inexpensive printing apparatus, and are rapidly becoming widespread.
Coloring materials for inks can be broadly classified into materials that use pigments and materials that use dyes. Of these, there is a growing tendency for the use of inks that use pigments as the coloring materials, as such inks exhibit the excellent levels of light resistance, weather resistance and water resistance that are required for high image quality printing.
In terms of the solvent, inks can be broadly classified into aqueous inks and non-aqueous inks. Non-aqueous inks that do not use water as the ink solvent, including solvent-based inks that use a volatile solvent as the main constituent and oil-based inks that use a non-volatile solvent as the main constituent, exhibit superior stability within the printer (such as intermittent dischargeability and discharge recovery following standing idle for a long period), cause no curling of the printed paper and have a short ink penetration and drying time, and are therefore attracting considerable attention.
In an inkjet recording system, the nozzle plate of the print head is frequently subjected to an ink repellent treatment using a fluorine-based process or the like, but because non-aqueous inks exhibit comparatively superior wettability of the nozzle plate, the nozzle plate tends to be wet comparatively easily by the ink. When ink adheres to the nozzle plate, the adhered ink hinders the discharge of ink droplets, and can cause problems such as discharge failure and discharge bending. Moreover, the adhered ink may also drip onto the paper, causing staining of the printed image.
Further, because the print head nozzles used in an inkjet recording system have very fine diameters and can sometimes become blocked, a cleaning mechanism is usually installed within the system. In one example of the cleaning mechanism, a small amount of ink is discharged, and a wiping blade is then used to wipe the surface of the nozzle plate. In this mechanism, because the ink is wiped off using the wiping blade, abrasion of the nozzle plate may cause a deterioration in the ink repellency of the nozzle plate, which can lead to the types of discharge faults described above.
Patent Document 1 discloses that by adding a salt of a long-chain polyamide and a polar acid ester, in an amount of at least 1% by mass relative to the total mass of the ink, to an oil-based inkjet ink comprising an ester-based solvent as the solvent, wetting of the nozzle plate by the ink can be inhibited. However, the Patent Document 1 includes no investigation of the deterioration in ink repellency caused by cleaning. Further, when a salt of a long-chain polyamide and a polar acid ester is added to an ink, the penetration of the ink into paper is accelerated, which may cause a reduction in the print density.
Moreover, in the case of a non-aqueous ink, the ink requires not only good wiping durability for the nozzle plate, but also requires a high print density and superior storage stability.
[Patent Document 1] JP 2008-274232 A
An object of the present invention is to provide a non-aqueous ink that exhibits excellent wiping durability for the nozzle plate, excellent storage stability, and superior print density, as well as providing a printing method that uses the ink and a method of producing the ink.